20 There are many causes of water _________ . For example, factories can dump waste into waterways, and broken pipes can allow pollutants into the water.
(A)treatment
(B)contamination
(C)storage
(D)distribution

水______的原因有很多。例如，工廠會將廢水排放到水道中，管道破裂也會導致污染物進入水中。